Combined heating and cooling systems are known in which a warm air furnace has associated therewith an air conditioning system having a cooling coil is placed in the air duct. However, such systems are essentially two complete systems, one a hot air heater which is relatively large and bulky and the other a complete air conditioner which is also relatively large and bulky.
It is also known that a common heat exchange liquid may be pumped throughout a large building to radiators having blowers associated therewith which will either blow hot or cold air depending on whether the liquid being circulated through the radiators has been heated or cooled by remotely located boilers or air conditioners.
Package heating and cooling units are also known where electric heating coils are placed in the cooling air ducts to heat the air when desired. However, such electric heat is neither economical nor sufficient for the total heating load in many areas of the country.